This disclosure relates to an array of airfoils within a stage of a gas turbine engine, for example, a turbine stator vane array.
A gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustor section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive the compressor and the fan section. The compressor section typically includes low and high pressure compressors, and the turbine section includes low and high pressure turbines.
The compressor and turbine section includes circumferential arrangements of fixed and rotating stages. Structural vibratory coupling between adjacent airfoils can occur during engine operation. For rotating stages of the engine, blade mistuning has been used in which there are two sets of blades are arranged in circumferentially alternating relationship to provide an even numbered blade array. One set of blades has a different characteristic than the other set of blades to provide two different resonant frequencies. For fixed stages, vanes have been mistuned by providing different sets of vanes in adjacent quadrants of the array.
A significant driver for turbine blade vibration is the pressure distortion produced by the interaction of the array of blades and the axially adjacent array of turbine vanes. As the blades pass the vanes, a pressure fluctuation occurs at the frequency at which the blades pass the vanes. Depending upon the distribution of pressure on the blades, certain blade vibratory modes may be excited if the blade/vane passing frequency matches the normal mode of the blade.